Reciprocating-piston internal combustion engines, which will in this context and hereinafter also be referred to in shortened form merely as internal combustion engines, have one or more cylinders in which a reciprocating piston is arranged. To illustrate the principle of a reciprocating-piston internal combustion engine, reference will be made below to FIG. 1, which illustrates by way of example a cylinder of a prior art internal combustion engine, which is possibly also a multi-cylinder internal combustion engine, together with the most important functional units.
The respective reciprocating piston 6 is arranged in linearly movable fashion in the respective cylinder 2 and, together with the cylinder 2, encloses a combustion chamber 3. The respective reciprocating piston 6 is connected by means of a so-called connecting rod 7 to a respective crankpin 8 of a crankshaft 9, wherein the crankpin 8 is arranged eccentrically with respect to the crankshaft axis of rotation 9a. As a result of the combustion of a fuel-air mixture in the combustion chamber 3, the reciprocating piston 6 is driven linearly “downward”. The translational stroke movement of the reciprocating piston 6 is transmitted by means of the connecting rod 7 and crankpin 8 to the crankshaft 9 and is converted into a rotational movement of the crankshaft 9, which causes the reciprocating piston 6, owing to its inertia, after it passes through a bottom dead center in the cylinder 2, to be moved “upward” again in the opposite direction as far as a top dead center.
To permit continuous operation of the internal combustion engine 1, during a so-called working cycle of a cylinder 2, it is necessary firstly for the combustion chamber 3 to be filled with the fuel-air mixture, for the fuel-air mixture to be compressed in the combustion chamber 3 and to then be ignited (by means of an ignition plug in the case of a gasoline internal combustion engine and by ultra-ignition in the case of a diesel internal combustion engine) and burned in order to drive the reciprocating piston 6, and finally for the exhaust gas that remains after the combustion to be discharged from the combustion chamber 3. Continuous repetition of this sequence results in continuous operation of the internal combustion engine 1, with work being output in a manner proportional to the combustion energy.
Depending on the engine concept, a working cycle of the cylinder 2 is divided into two strokes distributed over one crankshaft rotation (360°) (two-stroke engine) or into four strokes distributed over two crankshaft rotations (720°) (four-stroke engine). To date, the four-stroke engine has become established as a drive for motor vehicles. In an intake stroke, with a downward movement of the reciprocating piston 6, fuel-air mixture 21 (in the case of intake pipe injection by means of injection valve 5a, illustrated as an alternative in FIG. 1 by means of dashed lines) or else only fresh air (in the case of fuel direct injection by means of injection valve 5) is introduced from the air intake tract 20 into the combustion chamber 3.
During the following compression stroke, with an upward movement of the reciprocating piston 6, the fuel-air mixture or the fresh air is compressed in the combustion chamber 3, and if appropriate fuel is separately injected by means of an injection valve 5. During the following working stroke, the fuel-air mixture, for example in the case of the gasoline internal combustion engine, is ignited by means of an ignition plug 4, burns and expands, outputting work, with a downward movement of the reciprocating piston 6. Finally, in an exhaust stroke, with another upward movement of the reciprocating piston 6, the remaining exhaust gas 31 is discharged out of the combustion chamber 3 into the exhaust-gas tract 30.
The delimitation of the combustion chamber 3 with respect to the intake tract 20 or exhaust-gas tract 30 of the internal combustion engine is realized generally, and in particular in the example taken as a basis here, by means of inlet valves 22 and outlet valves 32. In the current prior art, said valves are actuated by means of at least one camshaft. The example shown has an inlet camshaft 23 for actuating the inlet valves 22 and has an outlet camshaft 33 for actuating the outlet valves 32. There are normally yet further mechanical components (not illustrated here) for force transmission provided between the valves and the respective camshaft, which components may also include a valve play compensation means (e.g. bucket tappet, rocker lever, finger-type rocker, tappet rod, hydraulic tappet etc.).
The inlet camshaft 23 and the outlet camshaft 33 are driven by means of the internal combustion engine 1 itself. For this purpose, the inlet camshaft 23 and the outlet camshaft 33, in each case by means of suitable inlet camshaft control adapters 24 and outlet camshaft control adapters 34, such as for example toothed gears, sprockets or belt pulleys, and with the aid of a control mechanism 40, which has for example a toothed gear mechanism, a control chain or a toothed control belt, are coupled, in a predefined position with respect to one another and with respect to the crankshaft 9 by means of a corresponding crankshaft control adapter 10, which is correspondingly formed as a toothed gear, sprocket or belt pulley, to the crankshaft 9. By means of this connection, the rotational position of the inlet camshaft 23 and of the outlet camshaft 33 in relation to the rotational position of the crankshaft 9 is, in principle, defined. By way of example, FIG. 1 illustrates the coupling between inlet camshaft 23 and the outlet camshaft 33 and the crankshaft 9 by means of belt pulleys and a toothed control belt.
The rotational angle covered by the crankshaft during one working cycle will hereinafter be referred to as working phase or simply as phase. A rotational angle covered by the crankshaft within one working phase is accordingly referred to as phase angle. The respectively current crankshaft phase angle of the crankshaft 9 can be detected continuously by means of a position encoder 43 connected to the crankshaft 9, or to the crankshaft control adapter 10, and an associated crankshaft position sensor 41. Here, the position encoder 43 may be formed for example as a toothed gear with a multiplicity of teeth arranged so as to be distributed equidistantly over the circumference, wherein the number of individual teeth determines the resolution of the crankshaft phase angle signal.
It is likewise additionally possible, if appropriate, for the present phase angles of the inlet camshaft 23 and of the outlet camshaft 33 to be detected continuously by means of corresponding position encoders 43 and associated camshaft position sensors 42. Since, owing to the predefined mechanical coupling, the respective crankpin 8, and with the latter the reciprocating piston 6, the inlet camshaft 23, and with the latter the respective inlet valve 22, and the outlet camshaft 33, and with the latter the respective outlet valve 32, move in a predefined relationship with respect to one another and in a manner dependent on the crankshaft rotation, said functional components run through the respective working phase synchronously with respect to the crankshaft.
The respective rotational positions and stroke positions of reciprocating piston 6, inlet valves 22 and outlet valves 32 can thus, taking into consideration the respective transmission ratios, be set in relation to the crankshaft phase angle of the crankshaft 9 predefined by the crankshaft position sensor 41. In an ideal internal combustion engine, it is thus possible for every particular crankshaft phase angle to be assigned a particular crankpin angle, a particular piston stroke, a particular inlet camshaft angle and thus a particular inlet valve stroke and also a particular outlet camshaft angle and thus a particular outlet camshaft stroke. That is to say, all of the stated components are, or move, in phase with the rotating crankshaft 9.
In modern internal combustion engines 1, there may be additional positioning elements within the mechanical coupling path between crankshaft 9 and inlet camshaft 23 and the outlet camshaft 33, for example in a manner integrated into the inlet camshaft adapter 24 and the outlet camshaft adapter 34, which positioning elements effect a desired controllable phase shift between the crankshaft 9 and inlet camshaft 23 and the outlet camshaft 33. These are known as so-called phase adjusters in so-called variable valve drives.
For optimum operation of the internal combustion engine (with regard to emissions, consumption, power, running smoothness, etc.), all operating variables relevant for efficient combustion of the fuel should be predefined and maintained as accurately as possible. The prior art for determining the operating variables is to measure a so-called reference internal combustion engine in all occurring operating states (engine speed, load, actuation of all actuators, different valve strokes, actuation of flaps, actuation of the phase adjusters for inlet and outlet valve, exhaust-gas turbocharger, compressor, etc.), and to store said measurement values (or derivatives thereof or model-based approaches which replicate the behavior) in corresponding characteristic maps in the engine control unit of a corresponding series-production internal combustion engine. All structurally identical, series-production internal combustion engines of the same type series are operated with this reference dataset that is generated. As a first approximation, the operating variables can thus be assumed as being known.
During the intended operation of a series internal combustion engine, however, component tolerances, wear phenomena, and/or environmental influences give rise to deviations of the actual operating variables from the operating variables sought on the basis of the reference data set. To counteract these deviations of the operating variables, it is necessary firstly to detect the actual operating variables and then perform adaptations in the reference data set or in the actuation for the purposes of a correction or approximation of the actual operating variables to the desired preset values.
Two important operating variables that consideration must be given to here are the injection start time and the obtained injection quantity of the fuel. Owing to tolerances in the injection valve itself (for example mechanical manufacturing tolerances) or in the electrical actuation thereof, deviations may arise between the desired and actual injection quantity of the fuel. Furthermore, deviations may arise between the desired injection start time and the actual injection start time of the injection. A quantity deviation leads to an impairment of the untreated emissions of the exhaust gas and thus possibly to a deterioration of the emissions of the overall system. An undesired shift of the injection time can, owing to the impairment of the mixture preparation, likewise lead to an impairment of the emissions.
It is therefore sought to detect the actual injection quantities and the injection start time as accurately as possible, to identify occurring deviations from the setpoint values (for example owing to tolerances), and to realize a corrective action by means of the adaptation of the actuation. Owing to ever-higher injection pressures, more complex injection valves and ever more stringent emissions requirements, this topic is of ever-increasing significance. In the case of the injection quantity and the injection start time, however, a direct detection/measurement of the present operating variables is not possible or can be determined only by indirect means. In the prior art, for this purpose, methods are proposed which perform a determination of the injection quantity for example on the basis of the pressure drop in the fuel supply or on the basis of dynamic torque fluctuations or on the basis of measurement values measured by means of a lambda probe. For the determination of the injection start times, methods are for example proposed which determine the injection start time on the basis of back-measurements of the current or voltage signal on an electrically driven injector and an analysis of the measured signal. Owing to the long functional chains, however, such methods are highly complex, susceptible to errors and inaccurate.